Update README

modify the markdown format

README

@@ -10,14 +10,17 @@ Guile csv reader
 sudo make install
 
 * read csv
+```scheme
 (use-modules (csv))
 (define my-csv-reader (make-csv-reader #:\,))
 (call-with-input-file "file.csv" my-csv-reader)
+```
 
 * csv->xml
 (call-with-input-file "file.xml" csv->xml)
 
 and file.xml could be:
+```xml
 <record-0>
  <name>aaa</name>
  <age>11</age>
@@ -28,8 +31,10 @@ and file.xml could be:
  <age>12</age>
  <email>bbb@bbb.com</email>
 </record-1>
+```
 
 * sxml->csv or csv-write to output a csv format file
+```scheme
 (call-with-output-file "file.csv"
  (lambda (port)
   (sxml->csv 
@@ -37,9 +42,9 @@ and file.xml could be:
    port)))
 
 and file.csv would be:
-
+```csv
 name,age,email
 aaa,11,aaa@aaa.com
 bbb,12,bbb@bbb.com
-
+```
 Enjoy!